igneous
Basalt
Mafic Igneous Pebble
Hardness: 6 on Mohs scale; Color: dark gray to black; Luster: dull/earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0; often contains microcrystalline plagioclase, pyroxene, and olivine.
- Hardness
- 6 on Mohs scale
- Color
- dark gray to black
- Luster
- dull/earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: dark gray to black; Luster: dull/earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0; often contains microcrystalline plagioclase, pyroxene, and olivine.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen appears water-worn, likely from a river or coastal environment, giving it a rounded shape.
Uses & applications
Commonly used in construction as aggregate for concrete, road base, and railroad ballast. Compact, weathered pieces like this are often collected as river stones or used for stone massage.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up most of the ocean floors. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its high density, dark color, and lack of visible individual crystals without magnification. Often found in volcanic regions or as weathered pebbles in glacial deposits and riverbeds.
